part 3] THE DEVONIAN OF FEEQTJES. 229 



in one band of limestone ; most of them are of ancient date, and 

 have been opened for building-stone, especially large blocks for 

 harbour-work and kerbing, and in the Middle Ages for forti- 

 fications. There are also a few isolated quarries. The shales are 

 being worked for bricks, and the sandstones for rough paving, 

 sills, etc. 



Physical Structure. 



Generally speaking, the beds consist of a number of parallel 

 "bands on the surface striking north-west and south-east, and this 

 •description has, up to the present, been accepted as sufficient. 

 Detailed investigation, however, shows that they are intersected 

 by a large number of dip-faults dividing the beds up into blocks 

 (step-faulting). The strike of the beds is, therefore, actually 

 more southerly than it appears to be from the general direction of 

 the strata ; the faulting gradually moves the beds in a northward 

 direction towards the west. In addition, there are a number of 

 •subordinate strike-faults (thrust-faulting), while a major thrust- 

 fault separates the Devonian from the Carboniferous. Former 

 ■observers have described the Carboniferous as lying conformably on 

 the Devonian, 1 or explain the absence of the uppermost Devonian 

 strata by a cessation of deposition. 



The general dip is south-westwards, varying from 20° to 45°, 

 with an average of about 30°. 



The limestones, sandstones, and dolomites usually project slightly 

 •above the general surface, forming small hills. 



Lower Palaeozoic beds (llouof/raptus-colon/is Zone) have been 

 found in a boring, a few hundred yards from the Devonian outcrop, 

 at Carriers, and in a shaft near the junction of the Mimoj'ecque and 

 Paradis roads, but their relations are masked by the overlying 

 'Cretaceous rocks. 



In addition to the main mass, there are smaller exposures at 

 Hydrequent, Sainte Grodeleine, and Ilougefort ; but, as the relations 

 of these outcrops form a part of the problem of the Carboniferous 

 deposits by which they are surrounded, they will not be considered 

 here, except generally and with a view to the elucidation of doubt- 

 ful questions relating to the main mass : they are regarded as being 

 bounded in the main by faults, although their actual structure 

 .appears to require further consideration. 



Palaeontology. 



No attempt is made in this paper to describe the palaeontology 

 "in detail. Owing to incorrect interpretation of the structure, it is 

 not always possible to ascertain in which bed specimens were 

 found ; the recorded forms are, therefore, of doubtful value in 

 .some cases. 



1 R. A. C. Godwin- Austen, Q. J. G. S. vol. ix (1853) p. 239. 



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